n = int(input())
a_ls = [int(a) for a in input().split()]

is_kadomatsu = lambda a, b, c: b > a > c or b > c > a or a > c > b or c > a > b
ans = len([True for i in range(n - 2) if is_kadomatsu(*a_ls[i:i + 3])])

print(ans)